Interface Modification of Polycrystalline Diamond Compact

ABSTRACT

A cutting element and a method of providing the cutting element are provided. The cutting element may include a substrate, a first polycrystalline diamond zone, and a second polycrystalline diamond zone. The first polycrystalline diamond zone may be substantially free of a catalyst material. The second polycrystalline diamond zone rich in the catalyst material may be bonded to the substrate along an interface. The second polycrystalline diamond zone may be bonded to the first polycrystalline diamond zone along an effective transition zone. The effective transition zone may have a plurality of irregular projections toward the first polycrystalline diamond zone and the second polycrystalline diamond zone.

BACKGROUND OF THE INVENTION

The present disclosure relates to polycrystalline diamond materials,and, more specifically, to polycrystalline composites and compacts whichare substantially free of a catalyzing material that have greatlyimproved impact resistance while maintaining excellent wear resistance.

It has become well known that the cutting properties of thepolycrystalline diamond materials are greatly enhanced when a relativelythin layer of the diamond material adjacent to a working surface istreated to remove the catalyzing material that remains there from themanufacturing process. This has been a relatively thin layer, generallyfrom about 0.05 mm to about 0.4 mm thick, and the depth from the workingsurface tends to be generally uniform. This type of polycrystallinediamond cutting element has now become nearly universally used ascutting elements in earth boring drill bits and has caused a verysignificant improvement in drill bit performance.

Because these surfaces tend to be planar, however, it has been observedthat fracture adjacent to the treated layer may occur. It has beenspeculated that the often lenticular type of fracture may be related tostresses that form in the area between the depleted and non-depletedregions. It is believed that stress concentrations in this ‘transition’region may lead to these fractures.

Therefore, there is a need for new approaches to the fabrication ofpolycrystalline composites and compacts with better performance.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a cutting element comprises:a first polycrystalline element zone having substantially free of acatalyst material; a second polycrystalline element zone rich in thecatalyst material; and an effective transition zone sandwiched betweenthe first polycrystalline element zone and the second polycrystallineelement zone, wherein the effective transition zone ranges from about 50to about 120 microns.

In another embodiment, a method comprises subjecting diamond crystal toa high pressure and high temperature condition in the presence of acatalyst material to form a polycrystalline diamond material; andtreating the polycrystalline diamond material to remove a portion of thecatalyst material to form a polycrystalline diamond body that has aneffective transition zone sandwiched between a first polycrystallinediamond zone having substantially free of a catalyst material and asecond polycrystalline element zone rich in the catalyst material,wherein the effective transition zone has a plurality of irregularprojections toward the first polycrystalline element zone and the secondpolycrystalline element zone.

In still another embodiment, a cutting element comprises: a substrate, afirst polycrystalline diamond zone having substantially free of acatalyst material; a second polycrystalline diamond zone bonded to thesubstrate along an interface, wherein the second polycrystalline diamondzone bonded to the first polycrystalline diamond zone along an effectivetransition zone, wherein the effective transition zone has a pluralityof irregular projections toward the first polycrystalline diamond zoneand the second polycrystalline diamond zone.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe embodiments, will be better understood when read in conjunction withthe appended drawings. It should be understood that the embodimentsdepicted are not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is schematic perspective view of a cylindrical shape PDC cuttingelement produced in a HPHT process according to an exemplary embodiment;

FIG. 2 is a schematic cross-sectional view of a machined PDC cuttercomprising a polycrystalline diamond and a substrate according toanother exemplary embodiment;

FIG. 3 is a schematic flow diagram illustrating a method of making a PDCcutter with an effective transition zone according to an exemplaryembodiment;

FIG. 4A is a scanning electron microscope (SEM) in back scatteredelectron mode of a polycrystalline diamond cutter made by a conventionalmethod;

FIG. 4B is a scanning electron microscope (SEM) in back scatteredelectron mode of a polycrystalline diamond cutter made by an exemplaryembodiment; and

FIG. 5 is a scanning electron microscope (SEM) in back scatteredelectron mode of a polycrystalline diamond cutter made by anotherexemplary embodiment.

DETAILED DESCRIPTION

Before the present methods, systems and materials are described, it isto be understood that this disclosure is not limited to the particularmethodologies, systems and materials described, as these may vary. It isalso to be understood that the terminology used in the description isfor the purpose of describing the particular versions or embodimentsonly, and is not intended to limit the scope. For example, as usedherein, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. In addition,the word “comprising” as used herein is intended to mean “including butnot limited to.” Unless defined otherwise, all technical and scientificterms used herein have the same meanings as commonly understood by oneof ordinary skill in the art.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as size, weight, reaction conditions and soforth used in the specification and claims are to the understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by theinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

As used herein, the term “about” means plus or minus 10% of thenumerical value of the number with which it is being used. Therefore,about 50% means in the range of 45%-55%. When the term, “substantiallyfree”, is used referring to catalyst in interstices, interstitialmatrix, or in a volume of polycrystalline element body, such aspolycrystalline diamond, it should be understood that many, if not all,the surfaces of the adjacent diamond crystals may still have a coatingof the catalyst. Likewise, when the term “substantially free” is usedreferring to catalyst on the surfaces of the diamond crystals, there maystill be catalyst present in the adjacent interstices.

The term “effective transition zone (ETZ)”, means the length between thehighest peak of a plurality of projections toward substantially leachedpolycrystalline element zone and the lowest valley of the plurality ofprojections toward rich in catalyst polycrystalline element zone.

Broadly, a cutting element may include ultra-hard particles. Theultra-hard particles may be those commonly used in the art and include,for example, diamond, cubic boron nitride and the like. The hardness ofthese particles is commonly a Knoop hardness number of 5,000 KHN orgreater. In one exemplary embodiment, a cutting element may be apolycrystalline element, such as polycrystalline diamond (PDC),polycrystalline diamond composite, polycrystalline cubic boron nitride(PcBN). In exemplary embodiments, polycrystalline diamond composite mayrepresent a volume of crystalline diamond grains with embedded foreignmaterial filling the inter-grain space. In one particular case,composite comprises crystalline diamond grains, bonded to each other bystrong diamond-to-diamond bonds and forming a rigid polycrystallinediamond body, and the inter-grain regions, disposed between the bondedgrains and filled with a catalyst material (e.g. cobalt or its alloys),which was used to promote diamond bonding during fabrication. Suitablemetal solvent catalysts may include the metal in Group VIII of thePeriodic table.

The cutting element comprises an above mentioned polycrystalline diamondbody attached to a suitable support substrate, e.g. cobalt cementedtungsten carbide (WC-Co), by the virtue of the presence of cobalt metal.In another exemplary embodiment, polycrystalline diamond compositecomprises a plurality of crystalline diamond grains, which are notbonded to each other, but instead are bonded together by foreign bondingmaterials such as borides, nitrides, carbides, etc. (e.g. SiC).

Polycrystalline diamond composites and the cutting element may befabricated in different ways and the following examples do not limit avariety of different types of diamond composites and cutters. In oneexemplary embodiment, cutters are formed by placing a mixture of diamondpolycrystalline powder with a suitable solvent catalyst material (e.g.cobalt) presented in WC-Co substrate. The assembly is subjected toprocessing conditions of extremely high pressure and high temperature(HPHT), where the solvent catalyst promotes desired inter-crystallinediamond-to-diamond bonding and, also, provides a binding betweenpolycrystalline diamond body and substrate support. In another exemplaryembodiment, the cutter is formed by placing diamond powder without acatalyst material on the top of substrate containing a catalyst material(e.g. WC-Co substrate or WC-Co substrate and an additional thin cobaltdisk facing the diamond powder). In this example, necessary cobaltcatalyst material is supplied from the substrate and melted cobalt isswept through the diamond powder during the HPHT process. In stillanother exemplary embodiment, a hard polycrystalline diamond compositeis fabricated by forming a mixture of diamond powder with silicon powderand mixture is subjected to HPHT process, thus forming a densepolycrystalline compact where diamond particles are bonded together bynewly formed SiC material.

Abrasion resistance of polycrystalline diamond composites and PDCcutters may be determined mainly by the strength of bonding betweendiamond particles (e.g. cobalt catalyst), or, in the case whendiamond-to-diamond bonding is absent, by foreign material working as abinder (e.g. SiC binder), or in still another case, by bothdiamond-to-diamond bonding and foreign binder. Presence of catalystinside the polycrystalline diamond body of the cutter promotes thedegradation of cutting edge of the cutter during the cutting process,especially if the edge temperature reaches a high enough critical value.Probably, this cobalt driven degradation is caused by large differencein thermal expansion between diamond and catalyst (e.g. cobalt metal),and also by catalytic effect of cobalt on diamond graphitization.Removal of catalyst from the polycrystalline diamond body of the cutter,for example, by chemical etching in acids, leaves interconnected networkof pores and a residual catalyst (up to 10 vol %) trapped inside thepolycrystalline diamond body. It has been demonstrated in previous artthat removal of cobalt from PDC cutter significantly improves itsabrasion resistance.

FIG. 1 shows schematic perspective view of a cutting element, such ascommon cylindrical shape PDC cutting element 12 produced in a HPHTprocess with a catalyst. Common PDC cutting element 12 comprises: asubstrate 20, which is made of hard metal, alloy, or composite, and mosttypically of cemented carbide or cobalt sintered tungsten carbide(WC-Co); and a polycrystalline diamond composite volume 14 rich incatalyst after the HPHT process, and attached or joined coherently tothe substrate along the interface 22. Very often, such catalyst ascobalt metal or its alloys may be present as a diamond bond forming aidin HPHT manufacture of the polycrystalline diamond volume 14. PDC cutterelement 12 may be later machined to a desired shape.

FIG. 2 shows a cross-sectional view of an exemplary embodiment of acutting element, such as a PDC cutter 12, a planar upper surface 24, achamfer 25, and a side surface 26. As it is appreciated, the shape ofPDC cutter described here does not limit the scope of current disclosureand PDC cutters may have a variety of shapes. Thus, in an exemplaryembodiment, the surface of machined PDC cutter 12 may be treated in amixture of acids in order to remove a surface layer of a catalyst. Thecutting element 12 may include a first polycrystalline element zone 27,a second polycrystalline element zone 21, and an effectivepolycrystalline element zone 28. The first polycrystalline element zone27 may have substantially free of a catalyst material. The secondpolycrystalline element zone 21 may be rich in a catalyst material.

The substrate 20, such as a cemented carbide substrate, for example, maybe configured to attach to the second polycrystalline element zone 21.The catalyst material may be present as a sintering aid in manufactureof the fist and the second polycrystalline element zones 27 and 21,respectively. The sintering aid may be a member selected from a groupcomprising of cobalt, nickel, and iron, for example. The first or secondpolycrystalline element zone 27 and 21 may comprise a material selectedfrom a group of polycrystalline cubic boron nitride, polycrystallinediamond and polycrystalline diamond like materials, such aspolycrystalline diamond doped with elements selected from a groupcomprising of N, B, P, Si, and S.

The diamond cutter 12 may comprise: the first polycrystalline elementzone 27 depleted in cobalt to a necessary one or several depths from,correspondingly: an outer peripheral upper surface 24, chamfer 25, or anouter peripheral side surface 26 of the polycrystalline diamondcomposite volume 21 rich in catalyst material, wherein the firstpolycrystalline element zone 27 extends along the side surface 26 to theeffective transition zone 28 with the second polycrystalline elementzone 21, but does not reach the interface 22 with the substrate 20. Inparticular cases, the first polycrystalline element zone 27 may extendaway from an upper surface 24 to a first predetermined depth, from achamfer 25 to a second predetermined depth, and from a side surface 26to a third predetermined depth.

For example, each depletion depth, as they were described above, may befrom about 10 μm to about 500 μm, or it could be from about 2 μm toabout 60 μm, for example. Also, for example, a third depletion depth mayconstitute of at least half of the overall thickness of thepolycrystalline diamond volume 21, but stops short of the interface 22by at least about 500 μm, for example.

Acid treated PDC cutter 12 may be taken out from hot acid bath, andcleaned in water to remove acid from the cutter 12. The interfacebetween the first polycrystalline element zone 27 and the secondpolycrystalline element zone 21 may be substantially linear as shown ina line 23 in FIG. 2 under conventional acid treatment. In an exemplaryembodiment, the effective transition zone 28 may exist between the firstpolycrystalline element zone 27 and the second polycrystalline elementzone 21. The effective transition zone 28 may be sandwiched between thefirst polycrystalline element zone 27 and the second polycrystallineelement zone 21. The effective transition zone 28 may range from about50 to about 120 microns, for example.

The effective transition zone 28 comprises a plurality of irregularprojections 29 and 31 toward the first polycrystalline element zone 27and the second polycrystalline element zone 21, respectively.

FIG. 3 illustrates a method of leaching a PDC cutting element accordingto an exemplary embodiment. In a step 32, a plurality of diamondcrystals may be subjected to a high pressure and high temperature(HPHT). More specifically, the plurality of diamond crystals may beloaded into a high pressure/high temperature cell and pressed in a beltpress apparatus at pressures of approximately 75 kbar and temperaturesof approximately 1500° C. During the step 32, the substrate may be usedas a source to introduce the catalyst, such as cobalt, during the highpressure high temperature condition. In a step 34, the polycrystallinediamond material may be treated to remove a portion of the catalystmaterial to form a polycrystalline diamond body that has an effectivetransition zone sandwiched between a first polycrystalline diamond zonehaving substantially free of a catalyst material and a secondpolycrystalline element zone rich in the catalyst material, wherein theeffective transition zone has a plurality of irregular projectionstoward the first polycrystalline element zone and the secondpolycrystalline element zone.

In the step 34, a leaching agent, such as a combination of acidsolution, for example, may be used. A group of techniques comprising ofelevated temperature, elevated pressure, ultrasonic energy, andcombination thereof, may be used in the step 34. In one exemplaryembodiment, the step of treating may comprise removing the catalystmaterial in an elevated temperature by using a leaching agent; andslowly cooling down the leaching agent and the polycrystalline diamondmaterial. In a treatment step 34, a catalyst, such as cobalt metal orits alloys, may be removed from the surface layer of the cutter bychemical etching in an acid solution, for example, in a mixture ofnitric and hydrofluoric acids, and subsequent cooling down to roomtemperature and cleaning of etching debris in water. In anotherexemplary embodiment, the treating step may further include masking apart of polycrystalline diamond material, such as masking a part at atop surface of the polycrystalline diamond material; and removing thecatalyst material in an elevated temperature by using a leaching agent.

The PDC cutting element 12 may be inserted into a fixture (not shown) sothat a protected portion 38 (shown in FIG. 2) which includes substrate20 and a part of polycrystalline diamond volume 12 (shown in FIG. 2) iscovered by the fixture, while a portion 36 (shown in FIG. 2) to beleached remains outside of the fixture.

According to an exemplary embodiment, the fixture may be formed frompolytetrafluoroethylene (PTFE). The PTFE may be unfilled or filled. Inother embodiments, the fixture may be formed from related organicpolymers, such as other fluoropolymers or fluoroplastics. Filled PTFEmay be filled with one or more of glass, molybdenum sulfide, bronze,acetal, carbon, such as graphite or carbon nanofibers, metal, metaloxides, mica, polyphenylene sulfide, and ceramic fillers, such as BaW04.Filled PTFE may also be Rulon®. Rulon® is a registered trademark ofSaint-Gobain Performance Plastics Corporation (Paris, France). Theprecise chemical composition of Rulon® is not publicly available.Another filled PTFE may be Amilon™, a graphite, glass, molybdenumsulfide, or carbon filled PTFE made by Plastomer Technologies (Houston,Tex.). The precise chemical composition of Amilon™ is also not publiclyavailable.

Fillers are typically added to PTFE to improve one or more of itsproperties. Accordingly, appropriate fillers for filled PTFE used in thefixture may be identified by adding the filler to PTFE, forming afixture from it, and testing the fixture for the desired property or forits general ability to protect non-leached portion. Such tests may beperformed under actual leaching conditions or approximate conditions.Similar tests may be used to identify other suitable fluoropolymers orfluoroplastics.

Without limiting the mechanism of the invention, PTFE may function wellas a fixture material due to its resistance to chemical reaction withacidic and caustic substances. The strong Carbon-Fluorine bond in PTFEallows Fluorine to form a non-reactive sheath surrounding the carbonchain. PTFE is also highly crystalline, making it difficult to dissolve.At present, there is no known solvent for PTFE. Thisgeneral-non-reactivity of PTFE may allow the fixture to withstandleaching process conditions and to be reused multiple times.Furthermore, the fixture may be able withstand leaching conditions forlong periods of time or at high temperature or pressure. In certainembodiments, other fluoropolymers or fluoroplastics selected for use asfixture may have a similarly low chemical reactivity with leachingagents and low solubility.

Also without limiting the mechanism of the invention, PTFE mayadditionally function well as a fixture material due to its low wettingproperties. PTFE has a wetting angle of 0, which means that water andaqueous solutions have virtually no tendency to move along PTFE viacapillary action. In the context of the current disclosure, this meansthat leaching agents effectively do not wick into the space between thefixture and protected portion of PDC element 12. Other fluoropolymers orfluoroplastics selected for use as the fixture may similarly have awetting angle of near zero.

The fixture may be formed by processing the protective material to thedesired configuration. In one embodiment, PTFE may be processed byheating granules of it to above 325° C., at which point it becomes aself-supporting gel that may be pressed, extruded, or sintered. Ingeneral, PTFE may be cut, bored or machined to very close tolerances. Inselected embodiments, rather than being made entirely of PTFE, thefixture may merely be coated entirely or in part with PTFE or it maycontain a PTFE portion.

The fixture may have an interior cavity that generally conforms to theshape of PDC cutting element 12. Due to the low wetting angle of PTFE(or other low wetting angle protective materials), the fixture mayalternatively have an interior cavity that is larger than the dimensionsof PDC element 12. In such an embodiment, only contact band may conformto the shape of PDC element 12. Due to the nearly complete absence ofcapillary action of water on PTFE, only a small, close-fitting contactband may be sufficient to substantially prevent the leaching agent fromreaching protected portion. Furthermore, the high resilience of PTFE mayallow the contact band to fit very closely to PDC cutting element 12and, in certain embodiments, to conform to the surface of PDC cuttingelement 12. Contact band may also be formed to precise tolerances,enhancing its ability to interface with PDC cutting element 12 in amanner to form a seal and substantially prevent wicking of the leachingagent.

In one particular embodiment, contact band may be formed from PTFE orother protective material and the exterior of the fixture may be coatedwith PTFE or other protective material, but the core of the fixture maybe formed from another material, which optionally may not be coated inthe interior cavity.

The use of a larger interior cavity in the fixture may offer variousadvantages, such as use of less PTFE or other protective material orgreater ease of removal of PDC element 12 from the fixture afterleaching. It is noted, however, that due to the low coefficient offriction of PTFE, neither insertion nor removal of PDC element 12 intoor out of the fixture tends to require substantial force. In mostinstances, the PDC element 12 may be inserted or removed by hand.

PDC cutting element 12 may be any type of element to be leached,including a cutter as shown in FIGS. 1 and 2. Leached portion maytypically be formed entirely of PDC. Protected, non-leached portion mayinclude some PDC; particularly PDC located at the interface of the PDCand substrate, and may also typically include the substrate.

EXAMPLE 1 Non-Linear Leached Interface in a PDC Cutter

A PDC cutter was produced under a high pressure high temperature method.Specifically, diamond particles having an average diameter ofapproximately 20 microns were loaded into a can material with a cobaltcemented tungsten carbide substrate having a non-flat interface. Thematerials were loaded into a high pressure/high temperature cell andpressed in a belt press apparatus at pressures of approximately 75 kbarand temperatures of approximately 1500° C. The resulting cutter had arange of diamond grain size averaged around 20 microns, surrounded bycobalt rich metal regions of varying size between the diamond grains.

The pressed cutter was finished to 16 mm in diameter with a diamondthickness of 2.1 mm, and a height of 8 mm. The cutter was then bonded toa tungsten carbide bonding stud to reach the overall height of 13 mm. A45 degree chamfer was placed on the edge of the diamond at a thicknessof 0.4 mm.

The cutter was then placed in a PTFE fixture and leached in theconventional way to a depth of 300 microns. The majority of metalresiding in the interstices between the diamond grains was removed by anacid etching process. In this case, the acid consisted of a mixture ofconcentrated nitric acid, hydrochloric acid, and hydrofluoric acid in avolume ratio of 3:9:4 respectively. To accelerate the leach, the acidmixture was heated to just below the boiling point, namely 185 F. Theleaching process was carried out over the period of 72 hours. At the endof the specified leaching time, conventionally, the cutters were removedfrom the hot acid and thoroughly washed to remove acid from the surface.

The cutters were cooled gradually in the acid, allowing for a range ofchemical activity and diffusion rates of the acid within the leach poresof the cutter. Specifically, allowing the cutter/fixture to reside inthe acid for 2.5 hours during which time the temperature of the acid wasgradually cooled from the normal leaching temperature of 185 F to roomtemperature, nominally 70 F. This gradual adjusting of the activity anddiffusion in the system allowed for the leaching process to continue inlarger leach pores for an extended period of time while smaller leachpores were slowed dramatically.

PDC cutters produced in this way were cut in half and examined in thescanning electron microscope (SEM) in back scattered electron mode toshow clear differentiation of the presence of metal or lack of metal,thereby allowing for an examination of the interface between the leachedand unleached PDC regions.

As shown in FIG. 4A, in conventionally leached PDC cutters of this type,the effective transition zone (ETZ), defined as the length between thehighest peak of the projections toward the first polycrystalline elementzone and lowest valley of the projections toward the secondpolycrystalline element zone, was on the order of one to two times ofthe diamond grain size. With a diamond grain size of approximately 20microns, the ETZ of a conventionally leached cutter was on the order of20-40 microns.

As shown in FIG. 4B, when the PDC cutters were leached using the methoddescribed in the exemplary embodiment, the EFT 28 was on the order ofthree to five times of the grain size. There was a plurality ofirregular projections 29, rich in catalyst material toward the firstpolycrystalline element. There was a plurality of irregular projectionsor valleys 31 toward the second polycrystalline element, withsubstantially free of the catalyst material. The plurality ofprojections 29 and 31 were randomly distributed by nature of the randompore size distribution. This translated to 60-100 microns, for example,between the highest and lowest leached points in the center region ofthe cutter. From the observed microstructure, the EFT for this examplewas 80 microns.

EXAMPLE 2 Abrasion Testing of Non-Linear Leach Interface

An exemplary embodiment provided a high abrasion resistance cuttersuitable for use in drilling and machining applications. Cuttersproduced as described in Example 1 have been tested on a verticaltorrent lathe (VTL) and show an improvement in abrasion resistance overcutters conventionally leached to the same depth. It is believed thatthis is due to two factors. Firstly, the larger EFT allows for a moregradual distribution of elastic properties in the cutting structure thana sharp, conventional interface between leached and unleached PDCcutter. This non-linear transition distributes the applied stress andthermally generated stress more gradually than a sharp transitionbetween leached and unleached. Secondly, the cutter from Example 1experienced a decrease in the amount of chipping observed in the test.This reduced chipping allowed for a smoother cutting surface, resultingin increased abrasion resistance.

EXAMPLE 3 Drop Test of Non-Linear Leach Interface

Cutters produced as described in Example 1 were dropped onto tungstencarbide in a standard drop test configuration. These cutters showedsigns of cracking around the point of impact, but these cracks did notpropagate far enough into the PDC cutter to lead to a large scalespallation of the leached diamond layer due to the undulating nature ofthe interface. When a conventionally leached cutter of the same leachdepth is dropped in the same configuration, large regions of the leacheddiamond spall off of the surface. With the near-linear conventionalinterface, there is little resistance to crack propagation along theweakened plane of the interface.

EXAMPLE 4 Interrupted Mill Test

Cutters were produced as described in Example 1. Samples withconventional and non-linear leach interfaces of nominally the same leachdepth were tested in an interrupted mill test. In this test, the cutterwas used to machine granite without the use of coolant, resulting inhigh heat generation in the cutter. Cutters were scored based on thenumber of passes across the 16″ rock before the cutter fails. Failure isdetermined as the cutter wearing through the diamond table and into thecarbide, at which point, the heat generated rapidly increases. Theconventionally leached cutter ran 4.53 passes before failure. The cutterof the disclosed invention ran 16.67 passes before failure, showing asignificant improvement in the thermal stability of the resultingcutter.

EXAMPLE 5 Masked Leaching to Provide Non-Linear Leaching Interface

Cutters were produced as described in Example 1, but prior to leachingprocess, a pattern of PTFE was applied to the top surface of the cutter.The applied pattern was designed not to prevent the leaching under themasked area, but rather to slow the leaching in the diamond immediatelyunder this masked regions by partially obstructing the pathway for theacid to access this region. In this example, a thin ring of PTFE waspainted onto the top surface of the cutter. After PTFE layer was cured,the cutter was placed in the fixture and underwent the conventionalleaching process described in Example 1. Cutters were sectioned andexamined in the SEM in back scattered electron mode as shown in FIG. 5

The result was a non-linearity in the transition from the firstpolycrystalline element having substantially free of a catalyst material27 (leached zone) to the second polycrystalline element zone rich in thecatalyst material 21 (unleached zone) which is regular and patterned bythe mask. In the present example, the masking was used to create asinusoidal leach front with a period of about 2 mm and an EFT of 126microns.

Although described in connection with preferred embodiments thereof, itwill be appreciated by those skilled in the art that additions,deletions, modifications, and substitutions not specifically describedmay be made without departure from the spirit and scope of the inventionas defined in the appended claims.

While reference has been made to specific embodiments, it is apparentthat other embodiments and variations can be devised by others skilledin the art without departing from their spirit and scope. The appendedclaims are intended to be construed to include all such embodiments andequivalent variations.

What is claimed is:
 1. A method, comprising the steps of: subjecting a plurality of diamond crystals to a high pressure and high temperature condition in the presence of a catalyst material to form a polycrystalline diamond material; and exposing a portion of the polycrystalline diamond material to a leaching agent at an elevated temperature for a first period of time and then gradually cooling the leaching agent and the polycrystalline diamond material to room temperature over a second period of time, thereby forming: a first polycrystalline diamond zone substantially free of the catalyst material, a second polycrystalline element zone rich in the catalyst material, and an effective transition zone sandwiched between the first and the second zones and having: a plurality of inter-grain regions that are substantially free of the catalyst material, a plurality of inter-grain regions that are rich in the catalyst material, and a plurality of irregular projections extending toward the first zone and the second zone a distance that is at least 3 times an average diameter of the grains.
 2. The method of claim 1, wherein the second period of time is greater than 1 hour.
 3. The method of claim 2, wherein the second period of time is greater than 2 hours.
 4. The method of claim 1, wherein the first period of time is greater than 48 hours.
 5. The method of claim 1, wherein the distance is less than or equal to about 5 times a size the average diameter of the grains.
 6. The method of claim 1, wherein the distance ranges from about 50 to about 120 microns.
 7. The method of claim 1, wherein: a substrate is also subjected to the high pressure and high temperature condition, and the substrate is a source of the catalyst material, and a polycrystalline diamond compact cutting element is formed.
 8. The method of claim 7, wherein the substrate is a cemented carbide substrate.
 9. The method of claim 1, wherein the leaching agent is a mixture of acids.
 10. The method of claim 9, wherein the elevated temperature is just below a boiling temperature of the acid mixture.
 11. The method of claim 1, wherein the catalyst material is selected from the group consisting of cobalt, nickel, and iron.
 12. The method of claim 1, further comprising inserting another portion of the polycrystalline diamond material into a protective fixture before exposure to the leaching agent.
 13. A method, comprising the steps of: subjecting a plurality of diamond crystals to a high pressure and high temperature condition in the presence of a catalyst material to form a polycrystalline diamond material; masking a portion of a top surface of the polycrystalline diamond material according to a pattern; and exposing at least the top surface of the polycrystalline diamond material to a leaching agent for a period of time, thereby forming: a first polycrystalline diamond zone substantially free of the catalyst material, a second polycrystalline element zone rich in the catalyst material, and an effective transition zone sandwiched between the first and the second zones and having a profile corresponding to the pattern.
 14. The method of claim 13, wherein the profile is sinusoidal. 